It is generally known that currently available motion control systems that are designed to move an object in more than one degree of freedom (DoF) include a separate motor or actuator for each DoF. More specifically, at least two motors or actuators are needed to implement 2-DoF motion, at least three motors or actuators are needed to implement 3-DoF motion, and so on. Consequently, mechanisms that involve more than one DoF tend to be somewhat large and cumbersome, and therefore inefficient.
While electronics and sensor technologies have gotten significantly smaller in recent years, mechanical motion technology has not kept up. This is why motion systems such as pan/tilt mechanisms are typically not used on smaller platforms, such as mini- or micro-UAVs (unmanned air vehicles) and micro-satellites. Robotics systems, which depend on multi-DoF motion control, must simply put up with the inherent inefficiencies of current motion-on-motion systems.
One solution to the above-described problems is disclosed in U.S. Pat. No. 7,675,208, entitled “Global Pointing Actuator.” The actuator disclosed therein includes a spherical stator with a “latitude coil” and a “longitude coil” wound thereon. This actuator, however, also exhibits certain drawbacks. For example, the longitude coil is physically difficult to wind. This is because the windings are not parallel and converge, or “bunch up,” at the poles of the spherical stator. This adds to the overall cost and size, and reduces coil efficiency. Another drawback is that a separate centering torque is (e.g., springs or a magnetic detent) required to implement open-loop position control of the armature.
Hence, there is a need for a multi-degree of freedom spherical actuator that is relatively smaller, less cumbersome, and more efficient than known devices and/or does not include coils that are difficult to wind and/or does not rely on a separate centering torque to implement open-loop position control of the armature. The present invention addresses at least these needs.